DESCRIPTION: Renal transplantation is the preferred therapeutic approach for end organ failure. However, the chronic use of immunosuppressive agents is critical to prevent rejection. The drugs are costly ($15,000-25,000/year) and have significant toxicities including opportunistic infection, an increased rate of malignancy, nephrotoxicity, and other end organ damage. The induction of donor-specific tolerance would address these limitations. Bone marrow chimerism induces tolerance to transplanted organs. However, the toxicity and complications associated with conventional hematopoietic stem cell transplants (HSCT), primarily graft-versus-host disease (GVHD) and the need for a matched donor, has limited the therapeutic application of HSCT to tolerance induction. We have identified and patented a novel tolerogenic bone marrow cell population of CD8+/TCR- facilitating cells (FC) that enhances engraftment of stem cells in mismatched recipients without causing GVHD. The discovery of FC opens the door to employing HSCT as a viable cell-based approach for tolerance induction. The product, FCRx, addresses the major challenges preventing the widespread use of HSCT for tolerance induction. FCRx is a bioengineered bone marrow product that includes hematopoietic stem cells (HSC) and FC, but avoids GVHD in mismatched recipients. In phase I of this proposal, we achieved our proposed milestones, demonstrating that we could reliably produce and transport FCRx and safely infuse it into nonmyeloablatively conditioned renal transplant recipients. We demonstrated that the proprietary FCRx procedure can routinely produce a graft with defined 12-TCR+ T cell composition and enriched for HSC and engraftment-enhancing FC. The ultimate goal is the induction of immune tolerance and the elimination of or reduction in the need for expensive and harmful immunosuppressive drugs. We have developed a nonmyeloablative conditioning regimen with 200 cGy TBI/fludarabine/cyclophosphamide/MMF/prograf to avoid the toxicity of conditioning. Since completing Phase I, we have addressed a major concern expressed by the reviewers regarding our ability to enroll subjects and have now successfully transplanted 6 living donor kidney patients, all of whom demonstrated donor chimerism at one month post-transplant. The approaches for collection, shipping, and FCRx preparation have also been approved by the FDA. Three patients show laboratory evidence of donor-specific tolerance, and immunosuppression is being weaned. The remaining subjects are early in follow-up. The reproducibility and quality assurance of the FCRx process will lead to its successful commercial launch. In phase II we will increase the pace of transplants and demonstrate that FCRx consistently achieves engraftment of HLA mismatched HSC in nonmyeloablatively conditioned kidney transplant recipients, induces donor-specific tolerance without causing significant GVHD, and reduces or eliminates the need for long-term immunosuppression. A recent meeting with FDA classified our product as Phase II, another milestone that will enhance commercialization.